CharEntityEncoderFallbackBuffer.cs

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using System.Runtime.CompilerServices;
using System.Text;
 
namespace System.Xml;
 
internal sealed class CharEntityEncoderFallbackBuffer : EncoderFallbackBuffer
{
    private readonly CharEntityEncoderFallback _parent;
 
    private string _charEntity = string.Empty;
 
    private int _charEntityIndex = -1;
 
    public override int Remaining
    {
        get
        {
            if (_charEntityIndex == -1)
            {
                return 0;
            }
            return _charEntity.Length - _charEntityIndex;
        }
    }
 
    internal CharEntityEncoderFallbackBuffer(CharEntityEncoderFallback parent)
    {
        _parent = parent;
    }
 
    public override bool Fallback(char charUnknown, int index)
    {
        if (_charEntityIndex >= 0)
        {
            new EncoderExceptionFallback().CreateFallbackBuffer().Fallback(charUnknown, index);
        }
        if (_parent.CanReplaceAt(index))
        {
            IFormatProvider formatProvider = null;
            IFormatProvider provider = formatProvider;
            Span<char> initialBuffer = stackalloc char[64];
            DefaultInterpolatedStringHandler handler = new DefaultInterpolatedStringHandler(4, 1, formatProvider, initialBuffer);
            handler.AppendLiteral("&#x");
            handler.AppendFormatted((int)charUnknown, "X");
            handler.AppendLiteral(";");
            _charEntity = string.Create(provider, initialBuffer, ref handler);
            _charEntityIndex = 0;
            return true;
        }
        EncoderFallbackBuffer encoderFallbackBuffer = new EncoderExceptionFallback().CreateFallbackBuffer();
        encoderFallbackBuffer.Fallback(charUnknown, index);
        return false;
    }
 
    public override bool Fallback(char charUnknownHigh, char charUnknownLow, int index)
    {
        if (!char.IsSurrogatePair(charUnknownHigh, charUnknownLow))
        {
            throw XmlConvert.CreateInvalidSurrogatePairException(charUnknownHigh, charUnknownLow);
        }
        if (_charEntityIndex >= 0)
        {
            new EncoderExceptionFallback().CreateFallbackBuffer().Fallback(charUnknownHigh, charUnknownLow, index);
        }
        if (_parent.CanReplaceAt(index))
        {
            IFormatProvider formatProvider = null;
            IFormatProvider provider = formatProvider;
            Span<char> initialBuffer = stackalloc char[64];
            DefaultInterpolatedStringHandler handler = new DefaultInterpolatedStringHandler(4, 1, formatProvider, initialBuffer);
            handler.AppendLiteral("&#x");
            handler.AppendFormatted(SurrogateCharToUtf32(charUnknownHigh, charUnknownLow), "X");
            handler.AppendLiteral(";");
            _charEntity = string.Create(provider, initialBuffer, ref handler);
            _charEntityIndex = 0;
            return true;
        }
        EncoderFallbackBuffer encoderFallbackBuffer = new EncoderExceptionFallback().CreateFallbackBuffer();
        encoderFallbackBuffer.Fallback(charUnknownHigh, charUnknownLow, index);
        return false;
    }
 
    public override char GetNextChar()
    {
        if (_charEntityIndex == _charEntity.Length)
        {
            _charEntityIndex = -1;
        }
        if (_charEntityIndex == -1)
        {
            return '\0';
        }
        return _charEntity[_charEntityIndex++];
    }
 
    public override bool MovePrevious()
    {
        if (_charEntityIndex == -1)
        {
            return false;
        }
        if (_charEntityIndex > 0)
        {
            _charEntityIndex--;
            return true;
        }
        return false;
    }
 
    public override void Reset()
    {
        _charEntityIndex = -1;
    }
 
    private int SurrogateCharToUtf32(char highSurrogate, char lowSurrogate)
    {
        return XmlCharType.CombineSurrogateChar(lowSurrogate, highSurrogate);
    }
}